He is so consumed by the matter that he studies congressional hearings on the Russia case, scrolling through them using TiVo. The night before dismissing Mr. Comey, he invited Time magazine journalists to dinner and, on a 60-inch-plus television he has had installed in the dining room, showed them various moments from the hearings, offering play-by-play-style commentary.

If Mr. Trump has nothing to hide, as he insists, he has only succeeded in making it appear as though he might. He seemed to almost invite comparisons to the Watergate scandal by firing Mr. Comey late in the day, then hosting Henry Kissinger in the Oval Office the next day. He offered contradictory explanations for his actions, making statements by his spokesmen inoperative, and finally made a veiled threat to Mr. Comey on Twitter, hinting that he might have secret tape recordings of their conversations.

“What we’ve really learned is either he’s worried about Russia because he’s got a significant vulnerability or he’s worried about Russia because it undermines his electoral win,” said Jennifer Palmieri, who was the communications director for Mrs. Clinton’s campaign. “He’s clearly been more preoccupied with it than we understood.”

Even setting aside the Russia investigation, Mr. Trump has seemed absorbed by his election victory, one that defied the odds and nearly all political prognostications. Since taking office, he has spoken regularly of his campaign triumph, even at events where it might not have seemed fitting, as during a visit to C.I.A. headquarters to discuss national security. In his first days in office, he was fixated on the size of his inauguration crowd.